1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices, and more particularly, to a method of manufacturing semiconductor devices having an effective channel of a target length.
2. Description of the Related Art
As the integration of semiconductor devices increases, their size becomes smaller. As a result, techniques for finely processing the same have been developed in the manufacturing process of semiconductor devices. Here, a photolithography process is a basic process for manufacturing semiconductor devices. The photolithography process greatly depends on materials or devices. In particular, when the photolithography process for forming a gate electrode of a transistor is performed, the length of the gate electrode can change by tens of nanometers in accordance with process conditions.
In the conventional art, a gate electrode composed of a gate insulating layer and a gate conductive layer is formed on a semiconductor substrate, and then a lightly-doped source and drain are formed by implantation using the gate electrode as a mask under conditions determined before manufacturing of the semiconductor device. When implantation for forming a source and drain is performed, implanted dopants are laterally diffused to the down-direction of the gate electrode. As a result, the length of the effective channel which is defined by the source and drain is reduced. Thus, the length of the channel which is formed under the gate electrode is determined by the length of the gate electrode and the lateral diffusion length of implanted dopants.
However, when the gate electrode is formed by photolithography, the length of the gate electrode typically varies in the order tens of nanometers depending on the process conditions. Even though the length of the gate electrode, the source and drain are implanted in accordance with implantation conditions which are determined before the process, so that the lateral diffusion length of implanted dopants are constant. Thus, the length of the effective channel formed under the gate electrode is proportional to the length of the gate electrode. That is, when devices are manufactured by conventional methods of semiconductor devices manufacturing, the length of the gate electrode is changed by conditions of the photolithography process and thus the length of the effective channel is changed.
However, when the length of the formed gate electrode is shorter than a target length, the length of the effective channel formed under the gate electrode becomes short to thereby deteriorate the yield rate. When the length of the formed gate electrode is longer than that of the target gate electrode, the length of the effective channel becomes long, thereby deteriorating the operational speed of the device.